In a conventional method of coating, as shown in FIG. 3 and FIG. 4a and 4b of the accompanying drawings, a single polar electrostatic charges applied on the surface of a support 2 by corona discharging from a corona discharging electrode 3 generated by a direct current high-voltage electric source 4, thereafter a liquid coating composition corresponding to a photographic light-sensitive material on a support 2 by means of a coating device is disclosed in U.S. Pat. No. 4,457,256 and a method of applying electrostatic discharging generated by a high-frequency high voltage on the surface of a support 2 to oxidize the surface of the support, wherein the surface of a grounded metal pass roller is insulated by a titanic acid series ceramic, etc., is disclosed in U.S. Pat. No. 4,649,097 and Japanese Patent Unexamined Publication No. Sho. 63-238139.
However, the method described in aforesaid U.S. Pat. No. 4,457,256 has the following problem. That is, since the surface of a grounded pass roller 1 is electrically conductive, it is required to reduce the length of the corona discharging electrodes 3 by .beta..perspectiveto.5 mm shorter than the width of the support 2 at each end thereof for preventing the occurrence of spark discharging between the corona discharging electrode 3 and the surface of the grounded pass roller 1 as shown in FIG. 4(a), thereby the surface potential of the support 2 is reduced at the vicinity .gamma. of each end as shown in FIG. 4(b), and hence the coating composition is liable to be cut at high speed coating to reduce the yield thereof.
Also, the methods described in U.S. Pat. No. 4,649,097 and Japanese Patent Unexamined Publication No. Sho. 63-238139 propose that a grounded pass roller is insulated by a ceramic for avoiding the occurrence of sparking as described above but since a high-frequency high voltage is employed as the discharging voltage, it is necessary to apply coating of the insulating material having a thickness of at least 0.5 mm onto the grounded pass roller for desirably preventing the occurrence of sparking. However, in the case of applying corona discharging to the support by a direct current high voltage, the discharging current is greatly reduced if such an insulating layer of grounded pass roller has such a thickness. Therefore, the conventional method can not be practically used for applying a desired surface potential to a support by corona discharging by d.c. high voltage.